1. Field of the Invention
The present invention relates particularly to a printer for positively detecting a presence or absence of printing paper fed in a printing portion of the printer.
2. Description of the Related Art
The conventional printer, as shown in FIG. 1, has a printing portion with a print head a and platen b which are oppositely arranged so that a printing paper P may be sandwiched there between. A ribbon guide c is attached to the print head a for guiding an ink ribbon R. On the platen b side of the printer, reflection-type paper detection sensors d are provided and arranged in a manner opposed to a printing paper P passing between the platen k and the ribbon guide c. The reflection-type paper detection sensors d are used to detect the presence or absence of the printing paper P. To accurately detect a presence or absence of a printing paper P, it is preferred that the paper detection sensors d are arranged as close as possible to a printing position. Accordingly, the paper detection sensors d are arranged in a position opposed to the ribbon guide c. When a printing paper P is not present, the light reflected on the ribbon guide c is received by the paper detection sensor d. To avoid erroneous detection of a printing paper P, the ribbon guide c is commonly manufactured with a black synthetic resin to minimize light reflection.
The conventional printer described above presents several problems which the present invention seeks to overcome. For example, the ribbon guide c is limited in color to black for minimization of light reflection. Also, the ribbon guide c comes in slide contact with the printing paper P. Accordingly, the ribbon guide c must be made of material that is highly resistant to wear. Thus, there has been a problem that the materials from which ribbon guide c may be made is quite limited. Furthermore, because the ribbon guide c is attached to the print head a as a heating member, it is desirable that the ribbon guide be made of a metal having a high heat dissipation effect. However, metal is highly reflective and will cause an intense reflection of light when a printing paper P is not present. The reflected light is received by the paper detection sensor d, thereby causing the printer to malfunction and to become unusable.
To solve the problems discussed above, the present invention implements a ribbon guide having a shape with sloped surfaces capable of reflecting the light emitted from a paper detection sensor to a position located away from the paper detection sensor in the absence of a printing paper. The ribbon guide is provided on a head block and has a sloped surface that is inclined relative to the surface of the printing paper.
When printing paper is not present between the paper detecting sensor and the ribbon guide, the light emitted from the paper detecting sensor is reflected off the sloped surface of the ribbon guide and is deflected to a position away from the paper detection sensor. As a result, the printer will not malfunction since the reflected light is not received by the paper detection sensor.
It is an object of the present invention to implement a ribbon guide for a printer having sloped surfaces which deflect light away from paper detection sensors when printing paper is not present.
It is another object of the present invention to implement a ribbon guide for a printer that may be made of desirable metals.
Other objects will become apparent from the foregoing description.
The present invention is directed toward a printer having a ribbon guide formed with a sloped surface that is inclined relative to a surface on which printing paper is fed. Accordingly, when a printing paper is not present between the paper detection sensor and the ribbon guide of the present invention, the light emitted from the paper detection sensor reflects off of these sloped surfaces toward a position away from the paper detection sensor. In essence, the present invention relies on the state of inclination of the sloped surface without relying upon a state of a surface of the ribbon guide. As a result, the present invention eliminates the possibility of erroneously detecting the presence or absence of printing paper, thus enabling stable detection of a printing paper. Because the ribbon guide""s surface state is not relied upon, various materials can be selected and used as a ribbon guide. The ribbon guide is preferably made of a metal. The use of a material high in thermal conductivity, such as aluminum enhances the effect of heat dissipation of the print head. Alternatively, the ribbon guide may be made of a material high in rigidity, such as magnesium. Highly rigid materials are desirable because the print head is driven together with the ribbon guide in a direction approaching the platen to urge the ribbon guide on a surface of a printing paper. The use of highly rigid materials will decrease the amount of deflection of the ribbon guide during the measurement of the paper thickness of a printing paper.